What is the recommended MRI protocol for evaluating suspected dementia?

MRI Protocol for Dementia Evaluation

MRI of the brain without intravenous contrast is the recommended imaging protocol for evaluating suspected dementia across all subtypes. 1

Standard Protocol Recommendation

Brain MRI without contrast is the appropriate initial imaging study for all dementia evaluations, including suspected Alzheimer disease, frontotemporal dementia, dementia with Lewy bodies, vascular dementia, and idiopathic normal-pressure hydrocephalus. 1 The most recent 2025 Alzheimer's Association guidelines explicitly state that brain MRI without contrast, when available and not contraindicated, is appropriate for evaluation of Alzheimer's disease and related dementias. 1

Key Technical Sequences

The MRI protocol should include:

• Three-dimensional T1-weighted volumetric imaging sequences for quantification of atrophy patterns and volumetric analysis of hippocampal, ventricular, and lobar volumes 2
• Fluid-attenuated inversion recovery (FLAIR) sequences for detection of white matter hyperintensities in vascular dementia 2
• Susceptibility-weighted imaging (SWI) sequences, preferably at 3.0T, for detection of microhemorrhages associated with cerebral amyloid angiopathy and vascular pathology 2
• Cine MRI sequences may be added when idiopathic normal-pressure hydrocephalus is suspected to assess aqueductal CSF flow dynamics 1

Clinical Utility of MRI in Dementia

Primary Diagnostic Roles

MRI serves multiple critical functions beyond simply excluding structural lesions:

• Excludes potentially reversible causes including tumors, inflammatory conditions, infectious processes, subdural hematomas, and normal-pressure hydrocephalus 1
• Identifies atrophy patterns that probabilistically suggest specific neurodegenerative diagnoses with high accuracy, though not as high as molecular biomarkers 1
• Detects microhemorrhages critical for patient selection and monitoring for amyloid-related imaging abnormalities (ARIA) in patients receiving disease-modifying antiamyloid therapies 1
• Changes clinical diagnosis in 23.7% of cases when combined with visual rating scales, primarily due to identification of vascular etiology 3

Specific Imaging Findings by Dementia Subtype

For Alzheimer disease: Look for atrophy in medial temporal lobes, lateral temporal and parietal cortices, with ventricular enlargement 1

For idiopathic normal-pressure hydrocephalus: Identify ventricular enlargement with Evans index >0.3 (maximal width of frontal horns/maximal width of inner skull), enlargement of temporal horns, callosal angle <90 degrees, and aqueductal flow void 1

For vascular dementia: Assess white matter hyperintensities using the Fazekas scale and identify strategic infarcts 4, 2

Visual Rating Scales

Semi-quantitative visual rating scales should be routinely applied when interpreting MRI scans for dementia evaluation:

• Medial temporal lobe atrophy (MTA) scale 4
• Fazekas scale for white matter changes 4
• Global cortical atrophy (GCA) scale 4

These scales significantly improve diagnostic accuracy and increase clinician confidence in the final diagnosis. 3

MRI vs. CT Comparison

While both MRI without contrast and CT without contrast are considered "usually appropriate" and equivalent alternatives by the ACR Appropriateness Criteria 1, MRI is strongly preferred when available due to:

• Higher sensitivity for detecting vascular lesions and specific dementia subtypes 4
• Superior ability to identify rare conditions causing dementia 4
• Better visualization of atrophy patterns and microhemorrhages 2

CT remains acceptable when MRI is contraindicated or unavailable, but MRI provides substantially more diagnostic information. 4, 5

Contrast Administration

Intravenous contrast is not needed for routine dementia evaluation. 1 All diagnostic findings relevant to dementia assessment, including atrophy patterns, ventricular enlargement, white matter changes, and microhemorrhages, are optimally visualized on noncontrast sequences.

Advanced Imaging Techniques

Advanced MR sequences including MR spectroscopy, functional MRI, and diffusion tensor imaging are NOT recommended for routine clinical use but may have value in research settings. 4 Similarly, quantification software for MRI is not recommended for routine clinical practice pending larger validation studies. 4

Important Clinical Caveats

• Potentially reversible dementia is rare, found in only 2.2% of patients, with less than 1% showing partial or full reversal 6, 5
• Most patients over age 80 with cognitive impairment harbor more than one type of brain pathological change, making mixed etiology dementia common 1
• MRI significantly increases clinician confidence in dementia subtype diagnosis even when the diagnosis doesn't change 3
• Specific molecular biomarkers remain necessary to confirm Alzheimer disease diagnosis and for treatment with disease-modifying therapy, despite supportive MRI findings 1